Syncope (Fainting)

Woman passed out on floor

Syncope is a temporary loss of consciousness usually related to insufficient blood flow to the brain. It's also called fainting or "passing out."

It most often occurs when blood pressure is too low (hypotension) and the heart doesn't pump enough oxygen to the brain. It can be benign or a symptom of an underlying medical condition.

What causes syncope?

Syncope is a symptom that can be due to several causes, ranging from benign to life-threatening conditions. Many non life-threatening factors, such as overheating, dehydration, heavy sweating, exhaustion or the pooling of blood in the legs due to sudden changes in body position, can trigger syncope. It's important to determine the cause of syncope and any underlying conditions.

However, several serious heart conditions, such as bradycardia, tachycardia or blood flow obstruction, can also cause syncope.

What is neurally mediated syncope?

Neurally mediated syncope (NMS) is the most common form of fainting and a frequent reason for emergency department visits. It's also called reflex, neurocardiogenic, vasovagal (VVS) or vasodepressor syncope. It's benign and rarely requires medical treatment.

NMS is more common in children and young adults, though it can occur at any age. It happens when the part of the nervous system that regulates blood pressure and heart rate malfunctions in response to a trigger, such as emotional stress or pain.

NMS typically happens while standing and is often preceded by a sensation of warmth, nausea, lightheadedness, tunnel vision or visual "grayout." Placing the person in a reclining position restores blood flow and consciousness, and ends the seizure.

Situational syncope, which is a type of NMS, is related to certain physical functions, such as violent coughing (especially in men), laughing or swallowing.

Other disorders can cause syncope, which also can be a side effect of some medicines.

Some types of syncope suggest a serious disorder:

  • Those occurring with exercise
  • Those associated with palpitations or irregularities of the heart
  • Those associated with family history of recurrent syncope or sudden death

What is cardiac syncope?

Cardiac or cardiovascular syncope is caused by various heart conditions, such as bradycardia, tachycardia or certain types of hypotension. It can increase the risk of sudden cardiac death.

People suspected of having cardiac syncope but who don't have serious medical conditions may be managed as outpatients. Further inpatient evaluation is needed if serious medical conditions are present. Conditions that may warrant hospital evaluation and treatment include various cardiac arrhythmic conditions, cardiac ischemia, severe aortic stenosis and pulmonary embolism. If evaluation suggests cardiac vascular abnormalities, an ambulatory external or implantable cardiac monitor may be required.

Heart failure, atrial fibrillation and other serious cardiac conditions can cause recurrent syncope in older adults, with a sharp increase after age 70.

What are the risk factors?

Syncope is common, but adults over age 80 are at greater risk of hospitalization and death.

Younger people without cardiac disease but who've experienced syncope while standing or have specific stress or situational triggers aren't as likely to experience cardiac syncope.

Cardiac syncope is a higher risk in: people older than age 60; men; presence of known heart disease; brief palpitations or sudden loss of consciousness; fainting during exertion; fainting while supine; an abnormal cardiac exam; or family history of inheritable conditions. Other existing conditions and medications used are particularly important in older patients.

AHA Recommendations

People who experience the warning signs of fainting of dizziness, nausea and sweaty palms should sit or lie down. Anyone with syncope should receive an initial evaluation, including detailed physical and history examinations and measurement of blood pressure and heart rate, by a physician.

An ECG (electrocardiogram) also is recommended as part of an initial evaluation to provide information about the cause of syncope. ECG is widely available and inexpensive and can provide information about the potential and specific cause of syncope (for example, abnormal heart rhythms). Other tests, such as exercise stress test, Holter monitor and an echocardiogram, may be needed to rule out other cardiac causes.

An ECG also is recommended for children and young adults with syncope. Other noninvasive diagnostic testing may be needed if they're suspected of having congenital heart disease, cardiomyopathy or a heart rhythm disorder.

If the initial evaluation is unclear, it may be useful for patients to undergo a tilt test. The blood pressure and heart rate will be measured while lying on a board and with the board tilted up. People with NMS usually will faint during the tilt, due to the rapid drop in blood pressure and heart rate. When people are placed on their back again, blood flow and consciousness are restored.

Patients with VVS and without a serious medical condition usually can be managed in an outpatient setting. For older adults, a comprehensive approach in collaboration with a geriatric expert can be helpful.

For people who are dehydrated, it may be beneficial to increase their salt and fluid intake to prevent syncope. That recommendation – as well as the removal or reduction of hypotensive drugs and diuretics – also is encouraged when appropriate and safe for people who've experienced situational syncope.

Consuming more salt and fluids can benefit most pediatric patients, but the results are unclear in people with NMS. Other lifestyle changes, such as exercise, also can benefit pediatric patients.

Some patients of any age may need medication.

When it comes to driving after a syncope episode, there are no restrictions for VVS patients who had no fainting spells in the previous year. Still, it may be helpful for healthcare providers to discuss regional driving laws, restrictions and implications with all patients.

For athletes, a cardiovascular assessment by a healthcare provider is recommended before resuming competitive sports. Those with syncope and a structural heart rhythm disorder should also see a specialist. Extended monitoring may help athletes with unexplained exertional syncope.

The Future of Syncope

Standardized national registries and large databases are needed to gather more data to better understand the incidence and prevalence of syncope, patient risks and outcomes, set lifestyle policies and improve healthcare delivery.

Some studies have shown that with recurrent episodes of fainting, the quality of life is reduced in both adults and in pediatric patients, however more well designed studies that incorporates quality of life, work loss and functional capacity are needed. In addition, more studies incorporate quality of life, work loss and functional capacity as possible results and better understand the relationship of syncope symptoms, causes and underlying diseases to various outcomes.